Method and apparatus for capturing, geolocating and measuring oblique images

ABSTRACT

A computerized system for displaying, geolocating, and taking measurements from captured oblique images includes a data file accessible by the computer system. The data file includes a plurality of image files corresponding to a plurality of captured oblique images, and positional data corresponding to the images. Image display and analysis software is executed by the system for reading the data file and displaying at least a portion of the captured oblique images. The software retrieves the positional data for one or more user-selected points on the displayed image, and calculates a separation distance between any two or more selected points. The separation distance calculation is user-selectable to determine various parameters including linear distance between, area encompassed within, relative elevation of, and height difference between selected points.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional PatentApplication Serial No. 60/425,275, filed Nov. 8, 2002.

TECHNICAL FIELD

[0002] The present invention relates to photogrammetry. Moreparticularly, the present invention relates to a method and apparatusfor capturing oblique images and for measuring the objects and distancesbetween the objects depicted therein.

BACKGROUND

[0003] Photogrammetry is the science of making measurements of andbetween objects depicted within photographs, especially aerialphotographs. Generally, photogrammetry involves taking images ofterrestrial features and deriving data therefrom, such as, for example,data indicating relative distances between and sizes of objects withinthe images. Photogrammetry may also involve coupling the photographswith other data, such as data representative of latitude and longitude.In effect, the image is overlaid and conformed to a particular spatialcoordinate system.

[0004] Conventional photogrammetry involves the capture and/oracquisition of orthogonal images. The image-capturing device, such as acamera or sensor, is carried by a vehicle or platform, such as anairplane or satellite, and is aimed at a nadir point that is directlybelow and/or vertically downward from that platform. The point or pixelin the image that corresponds to the nadir point is the only point/pixelthat is truly orthogonal to the image-capturing device. All other pointsor pixels in the image are actually oblique relative to theimage-capturing device. As the points or pixels become increasinglydistant from the nadir point they become increasingly oblique relativeto the image-capturing device and the ground sample distance (i.e., thesurface area corresponding to or covered by each pixel) also increases.Such obliqueness in an orthogonal image causes features in the image tobe distorted, especially images relatively distant from the nadir point.

[0005] Such distortion is removed, or compensated for, by the process ofortho-rectification which, in essence, removes the obliqueness from theorthogonal image by fitting or warping each pixel of an orthogonal imageonto an orthometric grid or coordinate system. The process ofortho-rectification creates an image wherein all pixels have the sameground sample distance and are oriented to the north. Thus, any point onan ortho-rectified image can be located using an X, Y coordinate systemand, so long as the image scale is known, the length and width ofterrestrial features as well as the relative distance between thosefeatures can be calculated.

[0006] Although the process of ortho-rectification compensates to adegree for oblique distortions in an orthogonal image, it introducesother undesirable distortions and/or inaccuracies in the ortho-rectifiedorthogonal image. Objects depicted in ortho-rectified orthogonal imagesmay be difficult to recognize and/or identify since most observers arenot accustomed to viewing objects, particularly terrestrial features,from above. To an untrained observer an ortho-rectified image has anumber of distortions. Roads that are actually straight appear curvedand buildings may appear to tilt. Further, ortho-rectified imagescontain substantially no information as to the height of terrestrialfeatures. The interpretation and analysis of orthogonal and/orortho-rectified orthogonal images is typically performed byhighly-trained analysts whom have undergone years of specializedtraining and experience in order to identify objects and terrestrialfeatures in such images.

[0007] Thus, although orthogonal and ortho-rectified images are usefulin photogrammetry, they lack information as to the height of featuresdepicted therein and require highly-trained analysts to interpret detailfrom what the images depict.

[0008] Oblique images are images that are captured with theimage-capturing device aimed or pointed generally to the side of anddownward from the platform that carries the image-capturing device.Oblique images, unlike orthogonal images, display the sides ofterrestrial features, such as houses, buildings and/or mountains, aswell as the tops thereof. Thus, viewing an oblique image is more naturaland intuitive than viewing an orthogonal or ortho-rectified image, andeven casual observers are able to recognize and interpret terrestrialfeatures and other objects depicted in oblique images. Each pixel in theforeground of an oblique image corresponds to a relatively small area ofthe surface or object depicted (i.e., each foreground pixel has arelatively small ground sample distance) whereas each pixel in thebackground corresponds to a relatively large area of the surface orobject depicted (i.e., each background pixel has a relatively largeground sample distance). Oblique images capture a generally trapezoidalarea or view of the subject surface or object, with the foreground ofthe trapezoid having a substantially smaller ground sample distance(i.e., a higher resolution) than the background of the trapezoid.

[0009] Oblique images are considered to be of little or no use inphotogrammetry. The conventional approach of forcing the variously-sizedforeground and background pixels of an oblique image into a uniform sizeto thereby warp the image onto a coordinate system dramatically distortsthe oblique image and thereby renders identification of objects and thetaking of measurements of objects depicted therein a laborious andinaccurate task. Correcting for terrain displacement within an obliqueimage by using an elevation model further distorts the images therebyincreasing the difficulty with which measurements can be made andreducing the accuracy of any such measurements.

[0010] Thus, although oblique images are considered as being of littleor no use in photogrammetry, they are easily interpreted and containinformation as to the height of features depicted therein.

[0011] Therefore, what is needed in the art is a method and apparatusfor photogrammetry that enable geo-location and accurate measurementswithin oblique images.

[0012] Moreover, what is needed in the art is a method and apparatus forphotogrammetry that enable the measurement of heights and relativeheights of objects within an image.

[0013] Furthermore, what is needed in the art is a method and apparatusfor photogrammetry that utilizes more intuitive and natural images.

SUMMARY OF THE INVENTION

[0014] The present invention provides a method and apparatus forcapturing, displaying, and making measurements of objects and distancesbetween objects depicted within oblique images.

[0015] The present invention comprises, in one form thereof, acomputerized system for displaying, geolocating, and taking measurementsfrom captured oblique images. The system includes a data file accessibleby the computer system. The data file includes a plurality of imagefiles corresponding to a plurality of captured oblique images, andpositional data corresponding to the images. Image display and analysissoftware is executed by the system for reading the data file anddisplaying at least a portion of the captured oblique images. Thesoftware retrieves the positional data for one or more user-selectedpoints on the displayed image, and calculates a separation distancebetween any two or more selected points. The separation distancecalculation is user-selectable to determine various parameters includinglinear distance between, area encompassed within, relative elevation of,and height difference between selected points.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above-mentioned and other features and advantages of thisinvention, and the manner of attaining them, will become apparent and bemore completely understood by reference to the following description ofone embodiment of the invention when read in conjunction with theaccompanying drawings, wherein:

[0017]FIG. 1 illustrates one embodiment of a platform or vehiclecarrying an image-capturing system of the present invention, and showsexemplary orthogonal and oblique images taken thereby;

[0018]FIG. 2 is a diagrammatic view of the image-capturing system ofFIG. 1;

[0019]FIG. 3 is a block diagram of the image-capturing computer systemof FIG. 2;

[0020]FIG. 4 is a representation of an exemplary output data file of theimage-capturing system of FIG. 1;

[0021]FIG. 5 is a block diagram of one embodiment of an image displayand measurement computer system of the present invention for displayingand taking measurements of and between objects depicted in the imagescaptured by the image-capturing system of FIG. 1;

[0022]FIG. 6 depicts an exemplary image displayed on the system of FIG.5, and illustrates one embodiment of the method of the present inventionfor the measurement of and between objects depicted in such an image;

[0023]FIGS. 7 and 8 illustrate one embodiment of a method for capturingoblique images of the present invention;

[0024]FIGS. 9 and 10 illustrate a second embodiment of a method forcapturing oblique images of the present invention.

[0025] Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate one preferred embodiment of the invention, in one form, andsuch exemplifications are not to be construed as limiting the scope ofthe invention in any manner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Referring now to the drawings, and particularly to FIG. 1, oneembodiment of an apparatus for capturing and geolocating oblique imagesof the present invention is shown. Apparatus 10 includes a platform orvehicle 20 that carries image-capturing and geolocating system 30.

[0027] Platform 20, such as, for example, an airplane, space shuttle,rocket, satellite, or any other suitable vehicle, carriesimage-capturing system 30 over a predefined area of and at one or morepredetermined altitudes above surface 31, such as, for example, theearth's surface or any other surface of interest. As such, platform 20is capable of controlled movement or flight, either manned or unmanned,along a predefined flight path or course through, for example, theearth's atmosphere or outer space. Image- capturing platform 20 includesa system for generating and regulating power (not shown) that includes,for example, one or more generators, fuel cells, solar panels, and/orbatteries, for powering image-capturing system 30.

[0028] Image-capturing and geo-locating system 30, as best shown in FIG.2, includes image capturing devices 32 a and 32 b, a global positioningsystem (GPS) receiver 34, an inertial navigation unit (INU) 36, clock38, gyroscope 40, compass 42 and altimeter 44, each of which areinterconnected with image-capturing computer system 46.

[0029] Image-capturing devices 32 a and 32 b, such as, for example,conventional cameras, digital cameras, digital sensors, charge-coupleddevices, or other suitable image-capturing devices, are capable ofcapturing images photographically or electronically. Image-capturingdevices 32 a and 32 b have known or determinable characteristicsincluding focal length, sensor size and aspect ratio, radial and otherdistortion terms, principal point offset, pixel pitch, and alignment.Image-capturing devices 32 a and 32 b acquire images and issue imagedata signals (IDS) 48 a and48 b, respectively, corresponding to theparticular images or photographs taken and which are stored inimage-capturing computer system 46, as will be more particularlydescribed hereinafter.

[0030] As best shown in FIG. 1, image-capturing devices 32 a and 32 bhave respective central axes A₁ and A₂, and are mounted to platform 20such that axes A₁ and A₂ are each at an angle of declination θ relativeto a horizontal plane P. Declination angle θ is virtually any obliqueangle, but is preferably from approximately 20° (twenty degrees) toapproximately 60° (sixty degrees) and is most preferably fromapproximately 40° (forty degrees) to approximately 50° (fifty degrees).

[0031] GPS receiver 34 receives global positioning system signals 52that are transmitted by one or more global positioning system satellites54. The GPS signals 52, in known fashion, enable the precise location ofplatform 20 relative to surface 31 to be determined. GPS receiver 34decodes GPS signals 52 and issues location signals/data 56, that aredependent at least in part upon GPS signals 52 and which are indicativeof the precise location of platform 20 relative to surface 31. Locationsignals/data 56 corresponding to each image captured by image-capturingdevices 32 a and 32 b are received and stored by image-capturingcomputer system 46.

[0032] INU 36 is a conventional inertial navigation unit that is coupledto and detects changes in the velocity, including translational androtational velocity, of image-capturing devices 32 a and 32 b and/orplatform 20. INU 36 issues velocity signals/data 58 indicative of suchvelocities and/or changes therein to image-capturing computer system 46,which stores velocity signals/data 58 corresponding to each imagecaptured by image-capturing devices 32 a and 32 b are received andstored by image-capturing computer system 46.

[0033] Clock 38 keeps a precise time measurement (time of validity) thatis used to synchronize events within image-capturing and geo-locatingsystem 30. Clock 38 provides time data/clock signal 62 that isindicative of the precise time that an image is taken by image-capturingdevices 32 a and 32 b. Time data 62 is also provided to and stored byimage-capturing computer system 46. Alternatively, clock 38 is integralwith image-capturing computer system 46, such as, for example, a clocksoftware program.

[0034] Gyroscope 40 is a conventional gyroscope as commonly found onairplanes and/or within commercial navigation systems for airplanes.Gyroscope 40 provides signals including pitch signal 64, roll signal 66and yaw signal 68, which are respectively indicative of pitch, roll andyaw of platform 20. Pitch signal 64, roll signal 66 and yaw signal 68corresponding to each image captured by mage-capturing devices 32 a and32 b are received and stored by image-capturing computer system 46.

[0035] Compass 42, such as, for example, a conventional electroniccompass, indicates the heading of platform 20. Compass 42 issues headingsignal/data 72 that is indicative of the heading of platform 20.Image-capturing computer system 46 receives and stores the headingsignals/data 72 that correspond to each image captured byimage-capturing devices 32 a and 32 b.

[0036] Altimeter 44 indicates the altitude of platform 20. Altimeter 44issues altitude signal/data 74, and image-capturing computer system 46receives and stores the altitude signal/data 74 that correspond to eachimage captured by image-capturing devices 32 a and 32 b.

[0037] As best shown in FIG. 3, image-capturing computer system 46, suchas, for example, a conventional laptop personal computer, includesmemory 82, input devices 84 a and 84 b, display device 86, and input andoutput (I/O) ports 88. Image-capturing computer system 46 executes imageand data acquiring software 90, which is stored in memory 82. Memory 82also stores data used and/or calculated by image-capturing computersystem 46 during the operation thereof, and includes, for example,non-volatile read-only memory, random access memory, hard disk memory,removable memory cards and/or other suitable memory storage devicesand/or media. Input devices 84 a and 84 b, such as, for example, amouse, keyboard, joystick, or other such input devices, enable the inputof data and interaction of a user with software being executed byimage-capturing computer system 46. Display device 86, such as, forexample, a liquid crystal display or cathode ray tube, displaysinformation to the user of image-capturing computer system 46. I/O ports88, such as, for example, serial and parallel data input and outputports, enable the input and/or output of data to and fromimage-capturing computer system 46.

[0038] Each of the above-described data signals is connected toimage-capturing computer system 46. More particularly, image datasignals 48, location signals 56, velocity signals 58, time data signal62, pitch, roll and yaw signals 64, 66 and 68, respectively, headingsignal 72 and altitude signal 74 are received via I/O ports 88 by andstored within memory 82 of image-capturing computer system 46.

[0039] In use, image-capturing computer system 46 executes image anddata acquiring software 90, which, in general, controls the reading,manipulation, and storing of the above-described data signals. Moreparticularly, image and data acquiring software 90 reads image datasignals 48 a and 48 b and stores them within memory 82. Each of thelocation signals 56, velocity signals 58, time data signal 62, pitch,roll and yaw signals 64, 66 and 68, respectively, heading signal 72 andaltitude signal 74 that represent the conditions existing at the instantan image is acquired or captured by image-capturing devices 32 a and 32b and which correspond to the particular image data signals 48 a and 48b representing the captured images are received by image-capturingcomputer system 46 via I/O ports 88. Image-capturing computer system 46executing image and data acquiring software 90 issues image-capturesignal 92 to image-capturing devices 32 a and 32 b to thereby causethose devices to acquire or capture an image at predetermined locationsand/or at predetermined intervals which are dependent at least in partupon the velocity of platform 20.

[0040] Image and data acquiring software 90 decodes as necessary andstores the aforementioned signals within memory 82, and associates thedata signals with the corresponding image signals 48 a and 48 b. Thus,the altitude, orientation in terms of roll, pitch, and yaw, and thelocation of image-capturing devices 32 a and 32 b relative to surface31, i.e., longitude and latitude, for every image captured byimage-capturing devices 32 a and 32 b is known.

[0041] Platform 20 is piloted or otherwise guided through animage-capturing path that passes over a particular area of surface 31,such as, for example, a predefined area of the surface of the earth orof another planet. Preferably, the image-capturing path of platform 20is at right angles to at least one of the boundaries of the area ofinterest. The number of times platform 20 and/or image-capturing devices32 a, 32 b pass over the area of interest is dependent at least in partupon the size of the area and the amount of detail desired in thecaptured images. The particular details of the image-capturing path ofplatform 20 are described more particularly hereinafter.

[0042] As platform 20 passes over the area of interest a number ofoblique images are captured by image-capturing devices 32 a and 32 b. Aswill be understood by those of ordinary skill in the art, images arecaptured or acquired by image-capturing devices 32 a and 32 b atpredetermined image capture intervals which are dependent at least inpart upon the velocity of platform 20.

[0043] Image data signals 48 a and 48 b corresponding to each imageacquired are received by and stored within memory 82 of image-capturingcomputer system 46 via I/O ports 88. Similarly, the data signals (i.e.,image data signals 48, location signals 56, velocity signals 58, timedata signal 62, pitch, roll and yaw signals 64, 66 and 68, respectively,heading signal 72 and altitude signal 74) corresponding to each capturedimage are received and stored within memory 82 of image-capturingcomputer system 46 via I/O ports 88. Thus, the location ofimage-capturing device 32 a and 32 b relative to surface 32 at theprecise moment each image is captured is recorded within memory 82 andassociated with the corresponding captured image.

[0044] As best shown in FIG. 1, the location of image-capturing devices32 a and 32 b relative to the earth corresponds to the nadir point N oforthogonal image 102. Thus, the exact geo-location of the nadir point Nof orthogonal image 102 is indicated by location signals 56, velocitysignals 58, time data signal 62, pitch, roll and yaw signals 64, 66 and68, respectively, heading signal 72 and altitude signal 74. Once thenadir point N of orthogonal image 102 is known, the geo-location of anyother pixel or point within image 102 is determinable in known manner.

[0045] When image-capturing devices 32 a and 32 b are capturing obliqueimages, such as oblique images 104 a and 104 b (FIG. 1), the location ofimage-capturing devices 32 a and 32 b relative to surface 31 issimilarly indicated by location signals 56, velocity signals 58, timedata signal 62, pitch, roll and yaw signals 64, 66 and 68, respectively,heading signal 72, altitude signal 74 and the known angle of declinationθ of the primary axes A₁ and A₂ of image-capturing devices 32 a and 32b, respectively.

[0046] It should be particularly noted that a calibration processenables image and data acquiring software 90 to incorporate correctionfactors and/or correct for any error inherent in or due toimage-capturing device 32, such as, for example, error due to calibratedfocal length, sensor size, radial distortion, principal point offset,and alignment.

[0047] Image and data acquiring software 90 creates and stores in memory82 one or more output image and data files 120. More particularly, imageand data acquiring software 90 converts image data signals 48 a, 48 band the orientation data signals (i.e., image data signals 48, locationsignals 56, velocity signals 58, time data signal 62, pitch, roll andyaw signals 64, 66 and 68, respectively, heading signal 72 and altitudesignal 74) into computer-readable output image and data files 120. Asbest shown in FIG. 4, output image and data file 120 contains aplurality of captured image files I₁, I₂, . . . , I_(n) corresponding tocaptured oblique images, and the positional data C_(PD1), C_(PD2), . . ., C_(PDn) corresponding thereto.

[0048] Image files I₁, I₂, . . . , I_(n) of the image and data file 120are stored in virtually any computer-readable image or graphics fileformat, such as, for example, JPEG, TIFF, GIF, BMP, or PDF file formats,and are cross-referenced with the positional data C_(PD1), C_(PD2), . .. , C_(PDn) which is also stored as computer-readable data.Alternatively, positional data C_(PD1), C_(PD2), . . . , C_(PDn) isembedded within the corresponding image files I₁, I₂, . . . , I_(n) inknown manner. Image data files 120 are then processed, either by imageand data acquiring software 90 or by post-processing, to correct forerrors, such as, for example, errors due to flight path deviations andother errors known to one of ordinary skill in the art. Thereafter,image data files 120 are ready for use to display and make measurementsof and between the objects depicted within the captured images,including measurements of the heights of such objects.

[0049] Referring now to FIG. 5, image display and measurement computersystem 130, such as, for example, a conventional desktop personalcomputer or a mobile computer terminal in a police car, includes memory132, input devices 134 a and 134 b, display device 136, and networkconnection 138. Image-capturing computer system 130 executes imagedisplay and analysis software 140, which is stored in memory 132. Memory132 includes, for example, non-volatile read-only memory, random accessmemory, hard disk memory, removable memory cards and/or other suitablememory storage devices and/or media. Input devices 134 a and 134 b, suchas, for example, a mouse, keyboard, joystick, or other such inputdevices, enable the input of data and interaction of a user with imagedisplay and analysis software 140 being executed by image display andmeasurement computer system 130. Display device 136, such as, forexample, a liquid crystal display or cathode ray tube, displaysinformation to the user of image display and measurement computer system130. Network connection 138 connects image display and measurementcomputer system 130 to a network (not shown), such as, for example, alocal-area network, wide-area network, the Internet and/or the WorldWide Web.

[0050] In use, and referring now to FIG. 6, image display andmeasurement computer system 130 executing image display and analysissoftware 140 accesses one or more output image and data files 120 thathave been read into memory 132, such as, for example, via networkconnection 138, a floppy disk drive, removable memory card or othersuitable means. One or more of the captured images I₁, I₂, . . . , I_(n)of output image and data files 120 is thereafter displayed as displayedoblique image 142 under the control of image display and analysissoftware 140. At approximately the same time, one or more data portionsC_(PD1), C_(PD2), . . . , C_(PDn) corresponding to displayed obliqueimage 142 are read into a readily-accessible portion of memory 132.

[0051] It should be particularly noted that displayed oblique image 142is displayed substantially as captured, i.e., displayed image 142 is notwarped or fitted to any coordinate system nor is displayed image 142ortho-rectified. Rather than warping displayed image 142 to a coordinatesystem in order to enable measurement of objects depicted therein, imagedisplay and analysis software 140, in general, determines thegeo-locations of selected pixels only as needed, or “on the fly”, byreferencing data portions C_(PD1), C_(PD2), . . . , C_(PDn) of outputimage and data files 120 and calculating the position and/orgeo-location of those selected pixels using one or more projectionequations as is more particularly described hereinafter.

[0052] Generally, a user of display and measurement computer system 130takes measurements of and between objects depicted in displayed obliqueimage 142 by selecting one of several available measuring modes providedwithin image display and analysis software 140. The user selects thedesired measurement mode by accessing, for example, a series ofpull-down menus or toolbars M, or via keyboard commands. The measuringmodes provided by image display and analysis software 140 include, forexample, a distance mode that enables measurement of the distancebetween two or more selected points, an area mode that enablesmeasurement of the area encompassed by several selected andinterconnected points, a height mode that enables measurement of theheight between two or more selected points, and an elevation mode thatenables the measurement of the change in elevation of one selected pointrelative to one or more other selected points.

[0053] After selecting the desired measurement mode, the user of imagedisplay and analysis software 140 selects with one of input devices 134a, 134 b a starting point or starting pixel 152 and an ending point orpixel 154 on displayed image 142, and image display and analysissoftware 140 automatically calculates and displays the quantity sought,such as, for example, the distance between starting pixel 152 and endingpixel 154.

[0054] When the user selects starting point/pixel 152, the geo-locationof the point corresponding thereto on surface 31 is calculated by imagedisplay and analysis software 140 which executes one or more projectionequations using the data portions C_(PD1), C_(PD2), . . . , C_(PDn) ofoutput image and data files 120 that correspond to the particular imagebeing displayed. The longitude and latitude of the point on surface 31corresponding to pixel 152 are then displayed by image display andanalysis software 140 on display 136, such as, for example, bysuperimposing the longitude and latitude on displayed image 142 adjacentthe selected point/pixel or in pop-up display box elsewhere on display136. The same process is repeated by the user for the selection of theend pixel/point 154, and by image display and analysis software 140 forthe retrieval and display of the longitude and latitude information.

[0055] The calculation of the distance between starting and endingpoints/pixels 152, 154, respectively, is accomplished by determining thegeo-location of each selected pixel 152, 154 “on the fly”. The dataportions C_(PD1), C_(PD2), . . . , C_(PDn) of output image and data file120 corresponding to the displayed image are retrieved, and thegeo-location of the point on surface 31 corresponding to each selectedpixel are then determined. The difference between the geo-locationscorresponding to the selected pixels determines the distance between thepixels.

[0056] As an example of how the geo-location of a given point or pixelwithin displayed oblique image 142 is determined, we will assume thatdisplayed image 142 corresponds to orthogonal image 104 a (FIG. 1). Theuser of image display and analysis software 140 selects pixel 154 which,for simplicity, corresponds to center C (FIG. 1) of oblique image 104 a.As shown in FIG. 1, line 106 extends along horizontal plane G from apoint 108 thereon that is directly below image-capturing device 32 a tothe center C of the near border or edge 108 of oblique image 104 a. Anextension of primary axis A₁ intersects with center C. Angle Ø is theangle formed between line 106 the extension of primary axis A₁. Thus, atriangle (not referenced) is formed having vertices at image-capturingdevice 32 a, point 108 and center C, and having sides 106, the extensionof primary axis A₁ and vertical (dashed) line 110 between point 108 andimage-capturing device 32 a.

[0057] Ground plane G is a substantially horizontal, flat or non-slopingground plane (and which typically will have an elevation that reflectsthe average elevation of the terrain), and therefore the above-describedtriangle includes a right angle between side/line 110 and side/line 106.Since angle Ø and the altitude of image-capturing device 32 (i.e., thelength of side 110) are known, the hypotenuse (i.e., the length of theextension of primary axis A₁) and remaining other side of the righttriangle are calculated by simple geometry. Further, since the exactposition of image-capturing device 32 a is known at the time the imagecorresponding to displayed image 142 was captured, the latitude andlongitude of point 108 are also known. Knowing the length of side 106,calculated as described above, enables the exact geo-location of pixel154 corresponding to center C of oblique image 104 a to be determined byimage display and analysis software 140. Once the geo-location of thepoint corresponding to pixel 154 is known, the geo-location of any otherpixel in displayed oblique image 142 is determinable using the knowncamera characteristics, such as, for example, focal length, sensor sizeand aspect ratio, radial and other distortion terms, etc.

[0058] The distance between the two or more points corresponding to twoor more selected pixels within displayed image 142 is calculated byimage display and analysis software 140 by determining the differencebetween the geo-locations of the selected pixels using known algorithms,such as, for example, the Gauss formula and/or the vanishing pointformula, dependent upon the selected measuring mode. The measurement ofobjects depicted or appearing in displayed image 142 is conducted by asubstantially similar procedure to the procedure described above formeasuring distances between selected pixels. For example, the lengths,widths and heights of objects, such as, for example, buildings, rivers,roads, and virtually any other geographic or man-made structure,appearing within displayed image 142 are measured by selecting theappropriate/desired measurement mode and selecting starting and endingpixels.

[0059] It should be particularly noted that in the distance measuringmode of image display and analysis software 140 the distance between thestarting and ending points/pixels 152, 154, respectively, isdeterminable along virtually any path, such as, for example, a“straight-line” path P1 or a path P2 that involves the selection ofintermediate points/pixels and one or more “straight-line” segmentsinterconnected therewith.

[0060] It should also be particularly noted that the distance measuringmode of image display and analysis software 140 determines the distancebetween selected pixels according to a “walk the earth” method. The“walk the earth method” creates a series of interconnected linesegments, represented collectively by paths P1 and P2, that extendbetween the selected pixels/points and which lie upon or conform to theplanar faces of a series of interconnected facets that define atessellated ground plane. The tessellated ground plane, as will be moreparticularly described hereinafter, closely follows or recreates theterrain of surface 31, and therefore paths P1 and P2 also closely followthe terrain of surface 31. By measuring the distance along the terrainsimulated by the tessellated ground plane, the “walk the earth” methodprovides for a more accurate and useful measurement of the distancebetween selected points than the conventional approach, which warps theimage onto a flat earth or average elevation plane system and measuresthe distance between selected points along the flat earth or plane andsubstantially ignores variations in terrain between the points.

[0061] For example, a contractor preparing to bid on a contract forpaving a roadway over uneven or hilly terrain can determine theapproximate amount or area of roadway involved using image display andanalysis software 140 and the “walk the earth” measurement methodprovided thereby. The contractor can obtain the approximate amount orarea of roadway from his or her own office without having to send asurveying crew to the site to obtain the measurements necessary.

[0062] In contrast to the “walk the earth” method provided by thepresent invention, the “flat earth” or average elevation distancecalculating approaches include inherent inaccuracies when measuringdistances between points and/or objects disposed on uneven terrain andwhen measuring the sizes and/or heights of objects similarly disposed.Even a modest slope or grade in the surface being captured results in adifference in the elevation of the nadir point relative to virtually anyother point of interest thereon. Thus, referring again to FIG. 1, thetriangle formed by line 106, the extension of primary axis A₁ and thevertical (dashed) line 110 between point 108 and image-capturing device32 a may not be a right triangle. If such is the case, any geometriccalculations assuming that triangle to be a right triangle would containerrors, and such calculations would be reduced to approximations due toeven a relatively slight gradient or slope between the points ofinterest.

[0063] For example, if surface 31 slopes upward between nadir point Nand center C at the near or bottom edge 108 of oblique image 104 thensecond line 110 intersects surface 31 before the point at which suchintersection would occur on a level or non-sloping surface 31. If centerC is fifteen feet higher than nadir point N and with a declination angleθ equal to 40° (forty degrees), the calculated location of center Cwould be off by approximately 17.8 feet without correction for thechange in elevation between the points.

[0064] As generally discussed above, in order to compensate at least inpart for changes in elevation and the resultant inaccuracies in themeasurement of and between objects within image 142, image display andanalysis software 140 references, as necessary, points within displayedimage 142 and on surface 31 to a pre-calculated tessellated or facetedground plane generally designated 160 in FIG. 6. Tessellated groundplane 160 includes a plurality of individual facets 162 a, 162 b, 162 c,etc., each of which are interconnected to each other and are defined byfour vertices (not referenced, but shown as points) having respectiveelevations. Adjacent pairs of facets 162 a, 162 b, 162 c, etc., sharetwo vertices. Each facet 162 a, 162 b, 162 c, etc., has a respectivepitch and slope. Tessellated ground plane 160 is created based uponvarious data and resources, such as, for example, topographical maps,and/or digital raster graphics, survey data, and various other sources.

[0065] Generally, the geo-location of a point of interest on displayedimage 142 is calculated by determining which of facets 162 a, 162 b, 162c, etc., correspond to that point of interest. Thus, the location of thepoint of interest is calculated based on the characteristics, i.e.,elevation, pitch and slope, of facets 162 a, 162 b, 162 c, etc., ratherthan based upon a flat or average-elevation ground plane. Error isintroduced only in so far as the topography of surface 31 and thelocation of the point of interest thereon deviate from the planarsurface of the facet 162 a, 162 b, 162 c, etc, within which the point ofinterest lies. That error is reducible through a bilinear interpolationof the elevation of the point of interest within a particular one offacets 162 a, 162 b, 162 c, etc., and using that interpolated elevationin the location calculation performed by image display and analysissoftware 140.

[0066] To use tessellated ground plane 160, image display and analysissoftware 140 employs a modified ray-tracing algorithm to find theintersection of the ray projected from the image-capturing device 32 aor 32 b towards surface 31 and tessellated ground plane 160. Thealgorithm determines not only which of facets 162 a, 162 b, 162 c, etc.,is intersected by the ray, but also where within the facet theintersection occurs. By use of bi-linear interpolation, a fairly preciseground location can be determined. For the reverse projection,tessellated ground plane 160 is used to find the ground elevation valuefor the input ground location also using bi-linear interpolation. Theelevation and location are then used to project backwards through amodel of the image-capturing device 32 a or 32 b to determine which ofthe pixels within displayed image 142 corresponds to the given location.

[0067] More particularly, and as an example, image display and analysissoftware 140 performs and/or calculates the geo-location of point 164 bysuperimposing and/or fitting tessellated ground plane 160 to at least aportion 166, such as, for example, a hill, of surface 31. It should benoted that only a small portion of tessellated ground plane 160 andfacets 162 a, 162 b, 162 c, etc., thereof is shown along the profile ofportion 166 of surface 31. As discussed above, each of facets 162 a, 162b, 162 c, etc., are defined by four vertices, each of which haverespective elevations, and each of the facets have respective pitchesand slopes. The specific position of point 164 upon the plane/surface ofthe facet 162 a, 162 b, 162 c, etc., within which point 164 (or itsprojection) lies is determined as described above.

[0068] Tessellated ground plane 160 is preferably created outside theoperation of image display and measurement computer system 130 and imagedisplay and analysis software 140. Rather, tessellated ground plane 160takes the form of a relatively simple data table or look-up table 168stored within memory 132 of and/or accessible to image display andmeasurement computer system 130. The computing resources required tocalculate the locations of all the vertices of the many facets of atypical ground plane do not necessarily have to reside within imagedisplay and measurement computer system 130. Thus, image display andmeasurement computer system 130 is compatible for use with andexecutable by a conventional personal computer without requiringadditional computing resources.

[0069] Calculating tessellated ground plane 160 outside of image displayand measurement computer system 130 enables virtually any level ofdetail to be incorporated into tessellated ground plane 160, i.e., thesize and/or area covered by or corresponding to each of facets 162 a,162 b, 162 c, etc., can be as large or as small as desired, withoutsignificantly increasing the calculation time, slowing the operation of,nor significantly increasing the resources required by image display andmeasurement computer system 130 and/or image display and analysissoftware 140. Display and measurement computer system 130 can thereforebe a relatively basic and uncomplicated computer system.

[0070] The size of facets 162 a, 162 b, 162 c, etc., are uniform in sizethroughout a particular displayed image 142. For example, if displayedimage 142 corresponds to an area that is approximately 750 feet wide inthe foreground by approximately 900 feet deep, the image can be brokeninto facets that are approximately 50 square feet, thus yielding about15 facets in width and 18 facets in depth. Alternatively, the size offacets 162 a, 162 b, 162 c, etc., are uniform in terms of the number ofpixels contained therein, i.e., each facet is the same number of pixelswide and the same number of pixels deep. Facets in the foreground ofdisplayed image 142, where the pixel density is greatest, wouldtherefore be dimensionally smaller than facets in the background ofdisplayed image 142 where pixel density is lowest. Since it is desirableto take most measurements in the foreground of a displayed image wherepixel density is greatest, creating facets that are uniform in terms ofthe number of pixels they contain has the advantage of providing moreaccurate measurements in the foreground of displayed image 142 relativeto facets that are dimensionally uniform.

[0071] Another advantage of using pixels as a basis for defining thedimensions of facets 162 a, 162 b, 162 c, etc., is that the locationcalculation (pixel location to ground location) is relatively simple. Auser operates image display and measurement computer system 130 toselect a pixel within a given facet, image display and analysis software140 looks up the data for the facet corresponding to the selected pixel,the elevation of the selected pixel is calculated as discussed above,and that elevation is used within the location calculation.

[0072] Generally, the method of capturing oblique images of the presentinvention divides an area of interest, such as, for example, a county,into sectors of generally uniform size, such as, for example, sectorsthat are approximately one square mile in area. This is done tofacilitate the creation of a flight plan to capture oblique imagescovering every inch of the area of interest, and to organize and namethe sectors and/or images thereof for easy reference, storage andretrieval (a process known in the art as “sectorization”). Because theedges of any geographic area of interest, such as a county, rarely fallson even square mile boundaries, the method of capturing oblique imagesof the present invention provides more sectors than there are squaremiles in the area of interest—how many more depends largely on thelength of the county borders as well as how straight or jagged they are.Typically, you can expect one extra sector for every two to three milesof border. So if a county or other area of interest is roughly 20 milesby 35 miles, or 700 square miles, the area will be divided intoapproximately from 740 to 780 sectors.

[0073] The method of capturing oblique images of the present invention,in general, captures the oblique images from at least two compassdirections, and provides full coverage of the area of interest from atleast those two compass directions. Referring now to FIGS. 7 and 8, afirst embodiment of a method for capturing oblique images of the presentinvention is shown. For sake of clarity, FIG. 7 and 8 is based on asystem having only one image-capturing device. However, it is to beunderstood that two or more image-capturing devices can be used.

[0074] The image-capturing device captures one or more oblique imagesduring each pass over area 200. The image-capturing device, as discussedabove, is aimed at an angle over area 200 to capture oblique imagesthereof. Area 200 is traversed in a back-and-forth pattern, similar tothe way a lawn is mowed, by the image-carrying device and/or theplatform to ensure double coverage of area 200.

[0075] More particularly, area 200 is traversed by image-carrying device32 and/or platform 20 following a first path 202 to thereby captureoblique images of portions 202 a, 202 b, and 202 c of area 200. Area 200is then traversed by image-carrying device 32 and/or platform 20following a second path 204 that is parallel and spaced apart from, andin an opposite direction to, i.e., 180° (one-hundred and eighty degrees)from, first path 202, to thereby capture oblique images of portions 204a, 204 b, 204 c of area 200. By comparing FIGS. 7 and 8, it is seen thata portion 207 (FIG. 8) of area 200 is covered by images 202 a-c capturedfrom a first direction or perspective, and by images 204 a-c capturedfrom a second direction or perspective. As such, the middle portion ofarea 200 is 100% (one-hundred percent) double covered. Theabove-described pattern of traversing or passing over area 200 alongopposing paths that are parallel to paths 202 and 204 is repeated untilthe entirety of area 200 is completely covered by at least one obliqueimage captured from paths that are parallel to, spaced apart from eachother as dictated by the size of area 200, and in the same direction aspaths 202 and 204 to thereby one-hundred percent double cover area 200from those perspectives/directions.

[0076] If desired, and for enhanced detail, area 200 is covered by twoadditional opposing and parallel third and fourth paths 206 and 208,respectively, that are perpendicular to paths 202 and 204 as shown inFIGS. 9 and 10. Area 200 is therefore traversed by image-carrying device32 and/or platform 20 following third path 206 to capture oblique imagesof portions 206 a, 206 b and 206 c of area 200, and is then traversedalong fourth path 208 that is parallel, spaced apart from, and oppositeto third path 206 to capture oblique images of portions 208 a, 208 b and208 c of area 200. This pattern of traversing or passing over area 200along opposing paths that are parallel to paths 206 and 208 is similarlyrepeated until the entirety of area 200 is completely covered by atleast one oblique image captured from paths that are parallel to, spacedapart from as dictated by the size of area 200, and in the samedirection as paths 206 and 208 to thereby one-hundred percent doublecover area 200 from those directions/perspectives.

[0077] As described above, image-carrying device 32 and/or platform 20,traverses or passes over area 200 along a predetermined path. However,it is to be understood that image-carrying device and/or platform 20 donot necessarily pass or traverse directly over area 200 but rather maypass or traverse an area adjacent, proximate to, or even somewhatremoved from, area 200 in order to ensure that the portion of area 200that is being imaged falls within the image-capture field of theimage-capturing device. Path 202, as shown in FIG. 7, is such a paththat does not pass directly over area 200 but yet captures obliqueimages thereof.

[0078] The present invention is capable of capturing images at variouslevels of resolution or ground sample distances. A first level ofdetail, hereinafter referred to as a community level, has a groundsample distance of, for example, approximately two-feet per pixel. Fororthogonal community-level images, the ground sample distance remainssubstantially constant throughout the image. Orthogonal community-levelimages are captured with sufficient overlap to provide stereo paircoverage. For oblique community-level images, the ground sample distancevaries from, for example, approximately one-foot per pixel in theforeground of the image to approximately two-feet per pixel in themid-ground of the image, and to approximately four-feet per pixel in thebackground of the image. Oblique community-level images are capturedwith sufficient overlap such that each area of interest is typicallycovered by at least two oblique images from each compass directioncaptured. Approximately ten oblique community-level images are capturedper sector.

[0079] A second level of detail, hereinafter referred to as aneighborhood level, is significantly more detailed than thecommunity-level images. Neighborhood-level images have a ground sampledistance of, for example, approximately six-inches per pixel. Fororthogonal neighborhood-level images, the ground sample distance remainssubstantially constant. Oblique neighborhood-level images have a groundsample distance of, for example, from approximately four-inches perpixel in the foreground of the image to approximately six-inches perpixel in the mid-ground of the image, and to approximately ten-inchesper pixel in the background of the image. Oblique neighborhood-levelimages are captured with sufficient overlap such that each area ofinterest is typically covered by at least two oblique images from eachcompass direction captured, and such that opposing compass directionsprovide 100% overlap with each other. Approximately one hundred (100)oblique area images are captured per sector.

[0080] It should be particularly noted that capturing oblique communityand/or neighborhood-level images from all four compass directionsensures that every point in the image will appear in the foreground orlower portion of at least one of the captured oblique images, whereground sample distance is lowest and image detail is greatest.

[0081] In the embodiment shown, image-capturing and geo-locating system30 includes a gyroscope, compass and altimeter. However, it is to beunderstood that the image-capturing and geo-locating system of thepresent invention can be alternately configured, such as, for example,to derive and/or calculate altitude, pitch, roll and yaw, and compassheading from the GPS and INU signals/data, thereby rendering one or moreof the gyroscope, compass and altimeter unnecessary. In fact,

[0082] In the embodiment shown, image-capturing devices are at an equalangle of declination relative to a horizontal plane. However, it is tobe understood that the declination angles of the image-capturing devicesdo not have to be equal.

[0083] In the embodiment shown, image-capturing computer system executesimage and data acquiring software that issues a common or singleimage-capture signal to the image-capturing devices to thereby causethose devices to acquire or capture an image. However, it is to beunderstood that the present invention can be alternately configured toseparately cause the image-capturing devices to capture images atdifferent instants and/or at different intervals.

[0084] In the embodiment shown, the method of the present inventioncaptures oblique images to provide double coverage of an area ofinterest from paths/perspectives that are substantially opposite to eachother, i.e., 180° (one-hundred and eighty degrees) relative to eachother. However, it is to be understood that the method of the presentinvention can be alternately configured to provide double coverage frompaths/perspectives that are generally and/or substantially perpendicularrelative to each other.

[0085] While the present invention has been described as having apreferred design, the invention can be further modified within thespirit and scope of this disclosure. This disclosure is thereforeintended to encompass any equivalents to the structures and elementsdisclosed herein. Further, this disclosure is intended to encompass anyvariations, uses, or adaptations of the present invention that use thegeneral principles disclosed herein. Moreover, this disclosure isintended to encompass any departures from the subject matter disclosedthat come within the known or customary practice in the pertinent artand which fall within the limits of the appended claims.

What is claimed is:
 1. A system for capturing images and geo-location data corresponding thereto, comprising: an image-capturing device, said image-capturing device capturing oblique images at image-capturing events, said image capturing device issuing image-data signals corresponding to captured images; at least one geo-locating device, each said at least one geo-locating device issuing a corresponding at least one geo-locating signal, each said at least one geo-locating signal being indicative at least in part of a geo-location of said image-capturing device during each image capturing event; and a computer system receiving and storing said image-data signals and said at least one geo-locating signal; and image and data acquiring software reading said image-data signals and said at least one geo-locating signal, said software associating each said image-data signal with a corresponding said at least one geo-locating signal for each image-capturing event.
 2. The system of claim 1, wherein said at least one geo-locating device and said at least one geo-locating signal respectively comprise at least one of: a clock issuing to said image-capturing computer system time data signals indicative of a time of each said image-capturing event; a global-positioning system (GPS) receiver receiving GPS signals and issuing to said image-capturing computer system location data signals indicative of a longitude and latitude of said image-capturing device at each said image-capturing event; an inertial navigation unit (INU) issuing to said image-capturing computer system velocity data signals indicative of a velocity of said image-capturing device at each said image-capturing event; a gyroscope issuing to said image-capturing computer system a pitch signal, a roll signal, and a yaw signal respectively indicative of a pitch, roll and yaw of said image capturing device at each said image-capturing event; a compass issuing to said image-capturing computer system heading data signals indicative of a heading of said image-capturing device at each said image-capturing event; and an altimeter issuing to said image-capturing computer system altitude data signals indicative of an altitude of said image-capturing device at each said image-capturing event.
 3. The system of claim 1, wherein said at least one geo-locating device and said at least one geo-locating signal respectively comprise: a clock issuing to said image-capturing computer system time data signals indicative of a time of each said image-capturing event; a global-positioning system (GPS) receiver receiving GPS signals and issuing to said image-capturing computer system location data signals indicative of a longitude and latitude of said image-capturing device at each said image-capturing event; an inertial navigation unit (INU) issuing to said image-capturing computer system velocity data signals indicative of a velocity of said image-capturing device at each said image-capturing event; a gyroscope issuing to said image-capturing computer system a pitch signal, a roll signal, and a yaw signal respectively indicative of a pitch, roll and yaw of said image capturing device at each said image-capturing event; a compass issuing to said image-capturing computer system heading data signals indicative of a heading of said image-capturing device at each said image-capturing event; and an altimeter issuing to said image-capturing computer system altitude data signals indicative of an altitude of said image-capturing device at each said image-capturing event.
 4. The system of claim 1, further comprising correction data indicative of characteristics of said image-capturing device including focal length, sensor size, radial distortion, principal point offset and alignment, said image and data acquiring software utilizing said correction data to correct captured images.
 5. The system of claim 1, further comprising an output data file created by said image and data acquiring software, said output data file including a plurality of image files and positional data corresponding to each of said plurality of image files.
 6. The system of claim 1, further comprising a platform carrying said image-capturing device a predetermined distance above a surface of interest.
 7. A computerized system for displaying, geolocating, and making measurements based upon captured oblique images, comprising: a computer system having a memory; an image and data file accessible by said system and including a plurality of image files corresponding to a plurality of captured oblique images, said image and data file further including positional data corresponding to said plurality of image files; image display and analysis software executed by said system for reading said image and data file and displaying at least a portion of the captured oblique images as a displayed image, said software retrieving said positional data of one or more selected points within said displayed image, said software calculating a separation distance between any two or more selected points within said displayed image.
 8. The system of claim 7, further comprising a ground plane data file representing a tessellated ground plane, said ground plane data file accessible by said computer system, said ground plane data file representing a tessellated ground plane that closely approximates at least a portion of the terrain depicted within said captured oblique images.
 9. The system of claim 8, wherein said tessellated ground plane further comprises a plurality of interconnected facets, each of said plurality of facets having a respective pitch and slope.
 10. The system of claim 9, wherein said ground plane data file comprises a plurality of vertices, each of said plurality of vertices having respective elevations and defining corners of said plurality of interconnected facets, two of said plurality of vertices shared by each of said interconnected facets.
 11. The system of claim 10, wherein said image display and analysis software identifies which of said plurality of facets corresponds to a selected point on said displayed image, and calculates an elevation of said selected point dependent at least in part upon the elevation of the vertices of the facet corresponding to the selected point, said image display and analysis software using said calculated elevation for calculating said separation distance between said selected point and one or more further selected points.
 12. The system of claim 11, wherein said image display and analysis software calculates a height of an object within said displayed image by calculating the separation distance between two or more selected points.
 13. The system of claim 8, wherein said tessellated ground plane is one of superimposed upon and fit to said displayed image.
 14. The system of claim 7, wherein said image display and analysis software includes user-selectable measuring modes accessible through at least one of pull-down menus, toolbars and keyboard commands.
 15. The system of claim 7, wherein each of said images were captured by an image-capturing device and at respective image capturing events, said positional data of said image and data file including: time data representing the time of each image-capturing event; location data representing the location of the image-capturing device at each image-capturing event; orientation data representing the orientation of the image-capturing device at each image-capturing event; correction data representing correction factors for the image-capturing device; and elevation data representing an average elevation of the surface captured by the image-capturing device.
 16. The system of claim 15, wherein said location data includes latitude, longitude, and altitude of the image-capturing apparatus at each image-capturing event.
 17. The system of claim 15, wherein said orientation data includes roll, pitch, yaw and heading of said image-capturing device at each image-capturing event.
 18. The data set of claim 15, wherein said image-capturing device is a camera and said correction data includes at least one of focal length, sensor size, aspect ratio, principle point offset, distortion, and pixel pitch.
 19. A computerized method for taking measurements within a displayed oblique image, comprising: selecting with an input device a starting point and an end point on the displayed image; retrieving from a data file positional data corresponding to said starting point and said end point; referencing a ground plane data file corresponding to a tessellated ground plane having a plurality of facets, each of said facets having a respective pitch and slope, said tessellated ground plane closely matching a terrain of said displayed oblique image; connecting said starting and end points with line segments, said line segments conforming to said pitch and slope of said facets to thereby follow said terrain; and calculating the linear distance along said line segments between said starting and end points thereby taking into account said pitch and slope of said facets.
 20. The method of claim 19, wherein said tessellated ground plane is superimposed upon said displayed oblique image.
 21. The method of claim 19, comprising the further steps of: selecting with an input device one or more intermediate points on the displayed image; retrieving from said data file positional data corresponding to said one or more intermediate points; and connecting adjacent intermediate points to each other, and connecting said starting and end points to adjacent intermediate points, with line segments, said line segments conforming to said pitch and slope of said facets to thereby follow said terrain; and calculating the distance along said line segments between said starting and end points.
 22. The method of claim 19, wherein said plurality of facets each correspond to equal areas of said displayed oblique image.
 23. The method of claim 19, wherein said plurality of facets each includes an equal number of pixels of said displayed oblique image.
 24. A computerized method for taking measurements from an oblique image displayed on a computer system, at least one input device connected to said computer system, an image data file accessible by said computer system, said image data file including captured images and positional data corresponding thereto, said computerized method comprising: placing the computer system into a desired one of a plurality of measurement modes, the desired measurement mode configured for calculating a desired measurement; selecting a starting point on the displayed image; retrieving the positional data corresponding to said starting point; selecting an end point on the displayed image; retrieving the positional data corresponding to said end point; and calculating the desired measurement dependent at least in part upon said positional data of said starting and end points.
 25. The method of claim 24, comprising the further steps of: selecting one or more intermediate points on said displayed image; and retrieving the positional data corresponding to said intermediate points.
 26. The method of claim 24, wherein said plurality of measurement modes comprise a distance measuring mode calculating a distance between two or more selected points, a height measuring mode calculating a height difference between two or more selected points, a relative elevation measurement mode calculating the difference in elevation of two or more selected points, and an area measurement mode calculating the area encompassed by at least three points.
 27. A method of capturing oblique images of an area of interest with an image-capturing device carried by a platform, each oblique image captured at a respective image-capturing event, said method comprising: subdividing the area of interest into a plurality of sectors; guiding the platform along a first path to thereby target one or more target sectors with the image-capturing device; capturing with the image-capturing device one or more oblique images to thereby cover an entirety of each said target sector in oblique images captured from a first perspective; guiding the platform along a second path to thereby target said target sectors; capturing with the image-capturing device one or more oblique images to thereby cover an entirety of each said target sector in oblique images captured from a second perspective; repeating said guiding and capturing steps along paths substantially parallel to and spaced apart from said first and second paths and capturing one or more oblique images to thereby cover an entirety of each of said plurality of sectors in oblique images captured from each of said first and second perspectives; and recording positional data indicative of a geo-location of said image-capturing device at each image-capturing event.
 28. The method of claim 27, wherein said second path is substantially parallel relative to and 180° (one-hundred and eighty degrees) from said first path;
 29. The method of claim 28, wherein said second path is also spaced apart from said first path.
 30. The method of claim 27, comprising the further steps of: guiding the platform along a third path to thereby target one or more target sectors with the image-capturing device, said third path being substantially perpendicular to said first and second paths; capturing with the image-capturing device one or more oblique images to thereby capture an entirety of each said target sector in oblique images captured from a third perspective; and repeating said guiding and capturing steps along paths substantially parallel to and spaced apart from said third path and capturing one or more oblique images to thereby cover an entirety of each of said plurality of sectors in oblique images captured from said third perspective.
 31. The method of claim 30, comprising the further steps of: guiding the platform along a fourth path to thereby target one or more target sectors with the image-capturing device, said fourth path being substantially parallel with said third path and 180° (one-hundred and eighty degrees) from said third path; capturing with the image-capturing device one or more oblique images to thereby capture an entirety of each said target sector in oblique images captured from a fourth perspective; and repeating said guiding and capturing steps along paths substantially parallel to and spaced apart from said fourth path and capturing one or more oblique images to thereby cover an entirety of each of said plurality of sectors in oblique images captured from said fourth perspective.
 32. The method of claim 31, wherein said fourth path is also spaced apart from said third path. 